1. Field of the Invention
The present invention relates to a ferroelectric thin film element fabrication method, and more particularly, to a method for fabricating a ferroelectric thin film, capable of preventing degradation due to fatigue and aging of a ferroelectric thin film of PZT and enabling crystallization at a low temperature.
2. Description of the Related Art
In general, PZT (PbZrxTi1-xO3) that is a perovskite ferroelectric material possesses excellent piezoelectric and ferroelectric properties. Thus, PZT is widely used for various semiconductor devices.
Recently, PZT applications are actively under study as in a FRAM (Ferroelectric Random Access Memory) for storing information by using polarization of PZT and a DRAM (Dynamic Random Access Memory) using a high dielectric constant of PZT deposited in the form of a thin film by means of sputtering, CVD, sol-gel, and so on.
However, applications of PZT have been limited owing to fatigue that makes polarization lower whenever a process of storing and reading information is repeated, aging that degrades properties as time passes, a low breakdown electric field and a high leakage current.
Attempts to reduce fatigue are made using an oxide electrode such as a RuO2 electrode instead of a Pt electrode, in which case a leakage current relatively increases.
Also, in the case of Bi group ferroelectric materials such as SBT (SrBi2Ta2O9) that are vividly under study for fabrication of a memory device together with PZT, degradation is not severe as PZT, but a high temperature for crystallization more than 700xc2x0 C. is required.
A low temperature process for preventing oxidation of a diffusion barrier and a uniform and fine grain size of a ferroelectric thin film for a uniform property of each element are required in addition to an excellent electric property in order to apply the ferroelectric thin film to a memory device.
Generally, a substrate should be heated higher than 300xc2x0 C., then PZT is deposited thereon, and a proper post-thermal treatment should be performed with a tubular furnace or a rapid thermal treatment apparatus after deposition when a PZT thin film is made to a perovskite phase having a polarization feature.
To solve the above problems, it is an object of the present invention to provide a ferroelectric thin film fabrication method capable of making a non-volatile memory device using an existing memory production facility, in which excellent polarization is maintained even after undergoing a number of cycles and a little amount of leakage current occurs using a ferroelectric thin film.
To accomplish the above object of the present invention, there is provided a ferroelectric thin film fabrication method comprising the steps of: forming a ferroelectric layer on one side of a semiconductor substrate; and performing an ion damage processing on the ferroelectric layer using an ionized gas.
A p-type or an n-type silicon substrate is used as the semiconductor substrate. The insulation layer is made of a silicon oxide layer produced by thermally oxidizing the silicon substrate. The electrode layer is made of platinum (Pt). The Pt layer is deposited with a thickness of 2000 xc3x85 on the semiconductor substrate whose temperature is maintained at 350xc2x0 C. and the Pt layer is deposited using a DC sputtering method with an argon gas.
The ferroelectric thin film fabrication method further comprises the step of forming an insulation layer on the side of the semiconductor substrate, prior to forming the ferroelectric layer.
The ferroelectric thin film fabrication method preferably further comprises the step of forming an electrode layer on the insulation layer, prior to forming the ferroelectric layer.
In addition, according to the invention, the electrode layer may be composed of at least one selected from the group consisting of Pt, Ir, IrO2, Ru, and RuO2.
The gas is made of one selected from the group consisting of argon, oxygen, nitrogen and hydrogen.
The ferroelectric layer is made of a ferroelectric material of ABO3 perovskite composite, in which A is made of at least one selected from the group consisting of lead (Pb), barium (Ba), and strontium (Sr), and B is made of at least one selected from the group consisting of zirconium (Zr) , titanium (Ti) , lanthanum (La) , and tungsten (W). The ferroelectric layer is formed with a thickness of 3000 xc3x85 in which the A and B metal targets are used and deposited with a reactive sputtering method using oxygen and argon gas. Before forming the ferroelectric layer, pre-sputtering is performed for 15-25 minutes using pure argon and then longer than 10 minutes using a mixture gas of oxygen and argon, thereby saturating surface oxidation of the target and making a deposition rate uniform.
The ferroelectric thin film layer may be also made of a ferroelectric material of Axe2x80x2BibMcO(2+3b+5c)/2, in which Axe2x80x2 is Ba, Sr or Pb and M is Ti, Ta or Nb.
In addition, the ferroelectric layer is Bi4-xLaxTi3O12(x=0xcx9c4).
The ferroelectric layer is formed by sol-gel process, sputtering process metal-organic chemical vapor deposition (MOCVD) process, or metal-organic decomposition (MOD) process.
At the ion damage processing step, the ion damage processing is performed using an ion mass doping system, in which an initial vacuum is maintained at 5xc3x9710xe2x88x926 torr, to thereby prevent an accelerated ion from scattering before reaching a test piece. After performing the ferroelectric ion damage processing, a post-annealing is performed at 300xcx9c800xc2x0 C. in an oxygen atmosphere.
As described above, the present invention performs an ion damage processing on a ferroelectric thin film such as PZT, to thereby enhance electrical properties such as polarization, fatigue, aging, leakage current and breakdown electric field. In particular, the present invention provides an advantage in productivity since crystallization can be made at low temperature.